Cronartium

Cronartium is a genus of rust fungi in the family Cronartiaceae. They are heteroecious rusts with two alternating hosts, typically a pine and a flowering plant, and up to five spore stages. Many of the species are plant diseases of major economic importance, causing significant damage. Some of the species have been introduced accidentally outside of their natural ranges, notably C. ribicola into North America, where it is an invasive species causing heavy mortality in several pines which have little or no resistance to it.